This invention relates generally to the field of spectrometers, and more specifically, to a spectrometer which is configured to provide simultaneous, multiple intensity spectra from independent light sources.
In many applications, it is desirable to be able to measure the thickness of a film at more than one location simultaneously. One such application is the manufacture of digital video disks (DVD) in which simultaneous measurement of film thickness over the surface of the disk helps to ensure a high degree of uniformity of film thickness in the final manufactured product. Another example is the manufacture and processing of semiconductor wafers. There, it is frequently desirable to deposit, using chemical vapor deposition (CVD) or the like, a film onto a substrate or a multi-film or patterned sample, or polish, using chemical mechanical planarization (CMP) or the like, an existing film on such a sample, such that the film has a high degree of uniformity in thickness.
Optical techniques for measuring the thickness of thin films by employing the reflectance spectra of light reflected from the film are detailed in the following co-pending U.S. patent applications, filed on even date herewith and having a common assignee with the subject application, each of which is hereby incorporated by reference herein as though set forth in full: 1.) "RAPID AND ACCURATE THIN FILM MEASUREMENT IN A NOISY ENVIRONMENT," U.S. patent application Ser. No. 09/210,148, "RAPID AND ACCURATE END POINT DETECTION IN A NOISY ENVIRONMENT," U.S. patent application Ser. No. 09/210,140; and 3.) "RAPID AND ACCURATE THIN FILM MEASUREMENT OF INDIVIDUAL LAYERS IN A MULTI-LAYERED OR PATTERNED SAMPLE," U.S. patent application Ser. No. 09/209,357. According to these techniques, reflected light from the film to be measured is passed through a spectrometer which dissects the reflected light into its constituent wavelengths. That it to say, it provides the intensity spectrum of the reflected light. A bank of photodetectors, which are frequently part of the spectrometer but can be independent thereof, receives the intensity spectrum, and provides an electrical signal for each wavelength of interest in which a parameter of the signal, most frequently amplitude, is representative of the intensity of the reflected light at that wavelength. A processor coupled to the photodetectors receives the electrical signals and, responsive thereto, determines a digitized version of the intensity spectrum, and then a thickness spectrum responsive to the digitized intensity spectrum. In one embodiment, the thickness spectrum is the Power Spectral Density (PSD) of the digitized intensity spectrum. In this embodiment, the estimated thickness of the film is taken to be the thickness corresponding to a selected peak of the PSD.
A problem thus arises because conventional spectrometers are capable of providing at a time the intensity spectrum of light reflected from only one portion of the surface of the film of interest. They are thus incapable of providing multiple simultaneous intensity spectra of light reflected from multiple portions of the surface of the film as required. Moreover, it is generally considered infeasible to use multiple conventional spectrometers in parallel, or alternatively, an optical multiplexor to allow sharing of a single spectrometer by multiple light sources, to provide the multiple simultaneous reflectance spectra as required.
Accordingly, there is a need for a spectrometer capable of providing multiple simultaneous intensity spectra from independent sources.